Dr. Constance Petersen (Ingrid Bergman) is a beautiful, unattached psychiatrist whose business-like facade fails to conceal a natural empathy that draws men. For her, however, love is a mere epi-phenomenon, easy to explain and resist, until she meets Dr. Edwardes (Gregory Peck). The famous expert on the guilt complex has arrived to replace the retiring chief (Leo Carroll). Constance is smitten, and so, it seems, is he.

But soon, she realizes that Edwardes is "not well," that he is terrified of dark lines on white: fork marks on a tablecloth; threads in her robe. Worse, she discovers that Edwardes is not, in fact, Edwardes, but an amnesic physician of initials "J. B." who is convinced that he has murdered his analyst. Constance does the right thing by having him removed from work, but she refuses to believe he is a murderer. Wanting to protect her, he leaves. But she, intent on curing her lover, follows him on a journey to retrace his last movements. The task is to recover both a memory and a missing person.

They go skiing (dark lines on white) at a resort where the real Dr. Edwardes had sojourned with his patient-colleague. On a dangerous slope, J. B. suddenly remembers that Edwardes went over the cliff. The body is found, but it has a bullet in the back.

Now hiding from the police, the couple pose as newlyweds and flee to her old mentor in Rochester. Complete with accent and beard, Dr. Brulov (Michael Chekhov) is a delightful double of the recently deceased Sigmund Freud (1858-1939). It emerges that John Ballantine (Peck) never lost his childhood feelings of guilt over the accidental death of his little brother.

In a gruesome ten-second flashback, the tyke is abruptly impaled on a iron-spike fence. This ancient guilt was reactivated by his doctor’s demise and it was sublimated by the defense mechanism of an assumed identity to keep the dead man alive. An idle slip of the tongue reveals the murderer to be the jealous retiree. The killer threatens Constance and then makes a quick end by dispatching himself instead.